Subsea equipment are traditionally made by putting electrical and/or electronic components designed for atmospheric pressure into a canister at 1 atm of pressure, in order to protect them from the high ambient subsea pressure.
In power electronics, this can cause heat generation in a range that are difficult, complicated or expensive to get rid of. Power losses normally generate an increase in the temperature of the whole system included in the canister. To improve the thermal conditions, the canister is exposed to a dielectric liquid at ambient pressure with the purpose of transporting heat losses to equipment surfaces which are cooled by the ambient water.
In subsea applications energy storage may require the use of capacitor banks including a plurality of electrolytic capacitors. Capacitor banks, when used in subsea applications, need, as explained above, to be inserted in the atmospheric pressure canisters described above, as these capacitors cannot withstand higher pressure. An alternative to electrolytic capacitors is that of using film capacitors or ceramic capacitors. The use of film capacitors or ceramic capacitors may be more critical than electrolytic capacitors, as these capacitors normally have a lower capacitance, i.e. they are more subject to failures and a greater number of them have to be used to obtain the same overall capacitance.
Particularly for medium bridging times lasting up to some seconds, the storage may consist or some or a huge amount of parallel connected capacitor components. No other electrical components are normally inserted in series with the capacitors, for not affecting the current value, when discharge of the capacitor bank is requested.
If one of the capacitors has a failure, for example a short circuit, it may happen that current flows through it, thus shorting the overall storage capacity of the capacitor bank. This may cause also other failures and therefore affects the reliability and lifetime of the whole system. This is of particular importance in subsea systems, which can be accessed with difficulty or with high costs after they have been put in operation.
In known solutions of bank capacitors for subsea electrical equipment, only huge capacitor banks are sectioned by means of fuses which are able, in order to avoid major inconvenience like electric arc formation, to exclude the capacitor bank as a whole. This kind of protection is normally not present in smaller banks (i.e. for voltage drives lower than 1000V), which are therefore not even sectioned.